Infrared carbon dioxide monitors, both mainstream and sidestream, have drawbacks: addition of a dead space, slow system response, and erroneous readings caused by the presence of nitrous oxide or oxygen, and by varying barometric pressure. To avoid the major shortcomings of existing capnometers, Physical Optics Corporation (POC) developed a proof-of-concept prototype Miniature Capnometer (MIC). The MIC is 2 mm in diameter, robust, and sensitive. It fits easily into the endotracheal tube, or into a sampling line of non-intubated patients. The device is immune to interference from other gases exhaled by the patient, to atmospheric pressure, and to humidity, and it has high carbon dioxide resolution and accuracy, and short response time. In Phase I we experimentally demonstrated MIC feasibility by fabricating a prototype and testing its parameters with a precise gas mixing system. In Phase II we will optimize the system design and performance parameters, and conduct in-depth testing during pressure and volume controlled conventional mechanical ventilation of rabbits with intact lungs under conditions of normocapnia, hypocapnia, and hypercapnia. The proposed miniature capnometer will overcome the major shortcomings of the existing infrared carbon dioxide monitors, including addition of a dead space, slow system response, and erroneous readings caused by the presence of nitrous oxide and oxygen, as well as varying brometric pressure. The proposed capnometer will be a robust, sensitive, and accurate tool for both hospital and pre-hospital applications, which will improve the treatment success and patient survival rate, all of which will contribute to public and individual health.